In the background art, several different ways are described, by means of which circuit modules containing components located inside an insulator material can be manufactured. The background art also discloses several solutions for manufacturing electrical contacts to the contact terminals of a component, by means of contact elements, and methods for manufacturing a conductor-pattern layer connected to the contact elements.
When evaluating circuit modules and manufacturing methods, attention can be paid, for example, to the circuit module's properties achieved by the method, for example, its price, mechanical durability, and the thickness (thinness) that can be achieved. Depending on the applications, significant factors can also be the quality and durability of the electrical contacts and the reliability and quality of the electrical properties of the whole module. Significant properties to be examined in terms of manufacturing can also be, for example, the reliability, yield, efficiency, price, and environmental friendliness of the manufacturing methods to be used. The practicability of the manufacturing method is also affected by the availability of raw materials and the ability of the method to place different types of component in a circuit module.
All in all, the requirements set for manufacturing methods and circuit modules are thus very diverse and vary according to the application. This being the case, there is still a need in the sector to develop new circuit-module structures and manufacturing methods, which can offer new or improved properties, or combinations of properties.
One line of development has been the placing of components inside the electronics module in a bumpless form, i.e. without growing bumps of top of the contact areas of the component. Cost benefits can then be gained, as the components need no longer be transported during manufacture to a separate production plant to make the bumps.
The applicant's own patent and application publications disclose manufacturing techniques, which can also be used in connection with bump-free components. The techniques described are particularly suitable for components, in which the material of the contact areas is copper. Of the applicant's own publications, those that can be referred to as most closely relating to the invention are the international patent application publications WO 2004/089048, WO 2005/027602, WO 2005/125298, WO 2006/013230, WO 2006/056643, WO 2006/134216, WO 2006/134217, and WO 2007/107630.
However, at present copper is quite little used as a conductor material in semiconductor processes. The most common conductor material is aluminium. In circuit-board manufacture, on the other hand, copper is the principal material for conductors. Copper conductors of a circuit module can be grown directly on top of aluminium contact areas, but the contact between copper and aluminium is brittle, so that a module of this kind is not optimal in applications, in which mechanical stress acts on the circuit module.
An improved possibility to use contact areas of aluminium or contact areas containing aluminium would mean that, in circuit modules and manufacturing methods, normal semiconductor circuits in a bumpless form could be used immediately after the semiconductor manufacturing processes and the passivation of the surface. As aluminium is the conductor material most widely used in the semiconductor industry, good compatibility between the contact element of the circuit module and aluminium would also ensure that suitable semiconductor circuits would be abundantly and economically available. Attempts to develop such manufacturing methods have indeed already been made for several decades in the field of component packaging technology. In component packaging solutions of this kind, the goal has been a technique, by means of which a relatively small component package could be manufactured around a component, to which a circuit board could then be attached later. Unlike packaging technology, the goal of the manufacturing techniques of the circuit module to which the present invention relates is the ability to manufacture the entire circuit board in the same process, so as to completely eliminate the packaging stage of the separate component. Of course, this does not exclude the possibility of using the manufacturing method of the circuit module to manufacture only a component package.
The U.S. Pat. No. 4,246,595, Noyori et al., discloses a method, in which the contact areas of a component are brought into contact with an insulator sheet, in which V-shaped openings have been made. First of all, a layer of titanium (Ti) or chromium (Cr) is grown on the surfaces of the openings and the aluminium contact areas. This intermediate metal layer is intended to prevent the copper from diffusing into the aluminium and the semiconductor component, as well as to improve the adhesion between the copper and the aluminium. In addition, the intermediate layer acts as an electrical conductor later during electrochemical growing (electroplating), so that the intermediate metal layer will reliably cover also the side walls of the openings. The growing of the titanium or chromium layer requires the use of the sputtering technique, for which reason the openings must also have a clear V shape. Sputtering is expensive when used on large surfaces (on circuit modules) while additionally the open V shape reduces the available conducting density. Contract structures of a corresponding type are also disclosed in U.S. Pat. No. 4,783,695 and U.S. Pat. No. 4,894,115, Eichelberger et al., and in U.S. Pat. No. 5,353,195, Fillion et al.
Later, in U.S. Pat. No. 6,396,148, Eichelberger at al., an attempt is made to solve the problems relating to sputtering, by forming the intermediate metal layer by growing a layer of nickel on the surface of the aluminium contact areas. According to the patent, the growing of the nickel is performed by means of a chemical growing method (electroless plating). Yet another layer, which also covers the side walls of the openings made in the insulating material for the contacts, is growing on top of the nickel layer by means of a chemical growing method. In the method, the components are attached first by their side and rear surfaces to the insulator layer and, after this, a photo-patternable polymer is spread on the front surface of the component and on top of the contact areas. The polymer is patterned by exposing it to light and developing it, to form openings for the contacts.
One possibility is to grow bumps on the surface of the conductors of the circuit-board part of the circuit module and attach the component to the conductors by a flip-chip mounting technique, for example, by ultrasound bonding. Such a method is disclosed in the applicant's own international patent application WO 2006/134220. Problems relating to both production and the quality of the contacts are associated with methods using flip-chip methods.